Reincarnated as Underswap Sans and how about Error get kidnapped instead?

1 - Baby bones... Eh? I'm older?

(Underswap Sans POV)

I was in my crib seeing baby papyrus in the other crib which is his own crib and got bored since I'm a baby bones and I'm like 1 year old in human age and monster age? Idk? 20 month maybe? Am I even younger or older brother? I didn't pay attention about the information of undertale. I snapped out as another skeleton which is Gaster looking at me worried. I thought this is a swapped au? This is probably a fanon au. He picked me up and went to the kitchen. 'I guess he thought that I was hungry...Wait, I am hungry!' I thought as Dad putting me down on a high chair and he prepared the baby food. 

After he prepared the baby food, he does the choo choo train in order feed me. I giggled before I eat. This is a bit weird that I'm acting like a baby acting. But hey. At least I can have an amazing childhood before the reset starts.

Time skip... (sorry lol)

Years have passed. I was now 10 years old and Papyrus was 5 years old, and Gaster? well... He went missing after the incident from the lab. I assumed he fell into the void but I'm not too sure of it.

I managed to get a job, working as a waiter at grillby's and to provide for me and my brother's needs. So I don't have to worry about getting starved to dust. The problem is that what am I suppose to do next since I'm underswap Sans. I started to think for a few moment and then it hit me. 'OH RIGHT! I should go join the royal guard in the future! But first, I need finish of schooling before joining. Papyrus as well, he needs to finish school.' I thought. I looked at the time was now 12:40 pm. I lock the door before I went outside while papyrus is playing in his room and going to work at grillby's. I open the door before going inside.

I closed the door and I heard a voice called me. "Sans?" I turned to see grillby and I could tell that he's worried. "O-Oh hey Grillby!" I said cheerfully. "You came here early?" "Mhm." "Are you sure about this? Aren't you supposed to be at school?" He said worriedly and I nodded before answering "Yes, I need money for me and my brother's needs and school? I was planning on that. Schools starts on next month, so I have time for that." Grillby sighed "Alright then, that's good. But don't overwork yourself, you're too young to work at this age." "Alright Grillbz!" he chuckled the nickname that I gave him. I started to work as the customers came in. Readers if you think that I wasn't wearing waiter uniform then you are wro- (Fresh: Hush Hush now.)

5 hours later

My shift work done and I already told Grillby that I needed to go home since I'm done working. Grillby told me that it was okay but I needed to go and I can't let my brother wait for longer. I change my waiter's clothes into my normal clothes. I opened the door and walk out before closing the door behind.

I was walking and passing by the christmas tree with gifts and other houses or stores. I finally arrived at home. I unlock the door and I open it to see Papyrus happy to see me. "Sans! You're home! Nyeheheh!" Papyrus ran up to me, tackled me with a hug and we laughed. "Myeheheh! Yes brother, I'm home..." "Sans, let's go watch a movie!" Papyrus said excitedly. I chuckled and I patted his skull. "Sure brother. But first, we must have dinner and then we could watch a movie" I said and Papyrus was jumping around happily then he went to the kitchen. I sighed and went to the kitchen as well. 

I started prepared the ingredients for the dish. 'Heh. I'm gonna make the best taco ever! Good thing I still have my cooking skills.' I thought and I started doing my cooking skills; cutting all the vegetables, boiling, putting pieces together and cooking. 

4 minutes later

I was done preparing for our dinner, putting down two plates of two tacos each side where me and my brother sit. I was about to call my brother, he shout as he hugged me after I turned. "SANS!" I almost jumped and I felt my soul is dropping. "P-Papyrus! Don't scare me like that!"
"O-oops. Sorry." He apologized and giggled. I sighed and patted his skull. "Next time, don't do that again" "No promises!" 'of course' I thought and I chuckled. "C'mon, sit down so we can have our dinner." he nodded and he sit down on his chair. I sat down and we took one taco on our plate and took a bite.

(Underswap Papyrus POV)

I took a bite of the taco and it tasted really good. My eye sockets was now watering with tears. I was now having a tears of joy. My brother's cooking was amazing! I chewed it and ate it. I wanted more but two tacos could make me full. My brother did a great job of cooking. I took the last taco on my plate, I bite it and chewed it. "Woah- Slow down, you might get choked." I did what my brother told until I'm done eating. 

"Alright brother, time for you to go to bed. Go brush your teeth first before going to bed." He said as he picked up the dished on the sink and he took the sponge and put it a soap on it. He started to wash the dishes. "Could you read me a bed time story when you're finished" I said as he he paused for a moment to think. "Hmm.... Alright. But go brush your teeth now and wait for me at your room" I giggled. I hugged him then I ran to the bathroom.

(2nd random person POV)

Sans chuckled as he continuing washing the dished. After a few minutes, he's done washing the dished. He picked up a story book which is "fluffy bunny" before he went up to stairs and walk to his brother's room. He opened the door and he sees his brother was already on his pj, he was lying on his bed and got himself tucked in. He went over to Papyrus bed and sit on it as he open the story book and started reading out loud.

After reading the story, he closed the book and he turned to see his brother was already asleep. He kissed on his brother's skull and said. "Goodnight brother, love you" He got up and walked out of his brother's room. He slowly closing the door without waking his brother.

He walks to his room and close it. He changed his clothes to his pj, he lay down on his bed and tucked himself. He closed his eye sockets and let the darkness takes over as he fell asleep. 

Edit:

Before he could fall asleep. He forgot that he and his supposed to watch a movie after dinner, but it doesn't matter anyway. Plus, he's tired.